1. Field of the Invention
The invention relates to a bottom structure of a personal watercraft (also called a PWC) in which very small concave or convex portions are provided on a bottom surface of the personal watercraft to enhance running performance and to reduce rolling of the watercraft.
2. Description of the Related Art
FIG. 13 shows an example of a hull shape of a conventional personal watercraft. The personal watercraft has a bottom surface 50 having a substantially V-shaped cross section. The bottom surface 50 is provided with a plurality of longitudinal strips 51. A rear part of the bottom surface 50 which forms a planing face of the personal watercraft is a smooth plane in a longitudinal direction of the bottom.
With the above-mentioned shape of the bottom surface 50, however, running performance such as accelerating performance, speed performance is limited due to fluid frictional resistance to water on a water contact face of the bottom during planing. Furthermore, if the water contact face of the watercraft varies between a right side and left side, a difference in dynamic outer forces received from the water flow on the right and left water contact surfaces is generated by repeated separation and sticking of the water on the right and left water contact faces. The difference in dynamic forces creates a difference of dynamic lift forces on the right and left side of the personal watercraft. Due to the difference between right and left dynamic lifts, repetition of small rolling is generated on the watercraft so that an uncomfortable feeling is sometimes given to a rider.
It is a main object of the invention to reduce frictional resistance to the water flow during the running of the personal watercraft, thereby enhancing the running performance.